Patients who develop metastases from melanoma in regional lymph nodes are known to be at high risk of developing further recurrences after surgical removal of the lymph node metastases. This study examines whether immunization over a two-year period with a vaccine made from vaccinia viral lysates of an allogeneic melanoma cell (VMCL), following surgical removal of lymph node metastases, would help prevent the development of distant metastases and improve survival from the disease. Eighty patients treated with VMCL alone and followed for a minimum of 5.5 years had improved survival compared with that of a historical control group of 151 patients and a concurrent nonrandomized group of 55 patients. Similarly, survival of 102 patients treated with VMCL plus low dose cyclophosphamide for a minimum of 3.5 years was superior to that of the historical control group but not to that of the group treated with VMCL alone. Improvement in survival measured from the date of removal of the primary tumor was still evident. Analysis of subsets of patients showed that VMCL treatment appeared to benefit patients irrespective of the number of lymph nodes involved and whether surgery was carried out near to (synchronous metastases) or some time after removal of the primary (delayed metastases). Analysis of two additional aspects provided further evidence for a biologic effect of the vaccine. One was an apparent alteration in distribution of metastases with a lower incidence of cutaneous metastases relative to visceral metastases in VMCL-treated patients. The second was a change in time to development of recurrences with a higher proportion of metastases occurring after 2 years in the treated patients. Of a projected 400 patients, 384 were entered into a randomized control (phase III) study to further evaluate this treatment. An interim analysis gave no reason for premature closure of the trial. This next analysis is scheduled for 9 months after closure of the trial.